An insulation material of this type is needed, for example, for the sheath of electrical and optical lines and cables or for the insulation of the cores themselves. Lines of this type include, for example, power lines or communications or data-transmission lines. The special insulation material is intended to ensure proper functioning of such a line in case of fire for a certain period of time. Machines, equipment, and apparatus must continue to be supplied with current during this period of time, and it should be possible to continue transmitting data during this time. The period of time should be sufficiently long, for example, to allow all persons present in a building to be informed and to keep the lights in the building turned on until the persons have left the building and possibly have also brought materials to safety. This period of time, which can be predetermined by the installer of lines of this type is, for example, between 30 minutes and 3 hours.
In the previously known line described in EP 0 106 708 B1, an insulation material is used that consists of mica wrap, a layer of polytetrafluoroethylene (PTFE), and a glass-fiber fabric coated with PTFE. The PTFE is resistant up to about 600° C. At higher temperatures, it disintegrates into ash. A line insulated in this way has an unacceptably high fire load in many cases. Due to the fluorine, it develops toxic and chemically aggressive gases (smoke) in a fire. These gases can attack and destroy metals and electrical and electronic circuits.
EP 0 968 502 A1 describes an insulation material for cables and lines that consists of a polymeric plastic as a first component, glass or ceramizable or crystalline material as a second component, and, for example, aluminum oxide as a third component. The second component is said to begin to melt at a temperature above the melting point of the first component, while the third component is said to melt at temperatures on the order of 1,000° C. This insulation material is supposed to maintain proper functioning of cables and lines in a temperature range of 450° C. to 1,210° C. The aforementioned, very different additives are added to the insulation material at relatively high expense, and for the most part they still require a transformation for a closed layer to be formed.
The previously cited document EP 0 978 128 B1 describes a fire-resistant insulation material for maintaining the function of electrical cables, in which glass frit from low-alkali glasses and passivation glass are added to an organosilicon polymer. Thus, only glass is added to the polymer for stabilization. According to this document, the low-alkali glasses have a melting point below 750° C., while the passivation glass has a melting point of not more than 710° C. In this insulation material, a glass layer that guarantees proper function is formed in the area of 700° C. The function can thus be maintained for a large temperature range starting at about 400° C. only for insulation materials based on organosilicon polymers which themselves start to melt only at relatively high temperatures to form a layer of glass.